A brushless motor used in, for example, a canned motor pump etc., such as an artificial heart pump, is configured such that the rotor is not fixed in the axial direction but is supported by hydrodynamic bearings or a magnetic bearing without contact therewith so as to be movable in the axial direction. In this case, to determine whether the rotor is at an appropriate position and to adjust the position of the rotor in the axial direction, it is necessary to detect the axial position of the rotor.
A known example of the method for detecting the axial position of the rotor involves detecting the position of the rotor on the basis of signals from a standard displacement sensor (optical, eddy-current type, capacitance type, etc.).
For example, in a motor incorporated in an axial-flow artificial heart pump, configured such that the rotor interacts with fluid flowing in a support tube, and provided with a regulator having a sensor for detecting the axial motion of the rotor and at least one electromagnetic coil, a technology for preventing step-out etc. of the motor by adjusting the magnetic field of the magnetic coil with the regulator has been proposed (for example, refer to Patent Citation 1).    Patent Citation 1: Japanese Translation of PCT International Application, Publication No. 2003-525561